This invention relates to gas analyzers for determining the presence and concentrations of gas components in a sample. The invention is especially adapted for use in the area of environmental measurements, such as engine emissions, although it may have other applications.
Using gas cells for calibration of optical gas benches has been described in the prior art. U.S. Pat. No. 5,060,505 describes an infrared-based device to measure gas concentration in which gas cells enclosing an amount of the component gas to be detected are selectively positioned in the optical path. While this device is very effective in eliminating the necessity for utilizing gases for calibration, it requires mechanical means to place and remove the gas cell in the optical path. The required mechanical means cannot be effectively used for measuring gas emissions of moving vehicles since they are quite sensitive to vibration.
An apparatus for detecting at least one component gas in a sample includes a source for providing radiation along at least one optical path in a pre-selected spectral band. The spectral band has at least one absorption line of the component gas to be detected. The apparatus further includes at least one optical detector positioned in the at least one optical path for detecting radiation in the pre-selected spectral band and for producing at least one detection output. A sample chamber is positioned in the at least one optical path between the source and the at least one detector and adapted to contain a quantity of sample gas including the component gas to be detected. A gas cell enclosing an amount of component gas to be detected is permanently positioned in the at least one optical path in series with the sample chamber. A control includes an algorithm for determining a mathematical relationship between the at least one detector output and the concentration of a sample gas filling the sample chamber.
A method for detecting at least one component gas in a sample, according to an aspect of the invention, includes providing radiation along at least one optical path in a pre-selected spectral band. The spectral band has at least one absorption line of the component gas to be detected. The method further includes detecting radiation in the at least one optical path in the pre-selected spectral band. The method further includes positioning a sample chamber in the at least one optical path. The sample chamber is adapted to contain a quantity of sample gas including the component gas to be detected. The method further includes fixedly positioning at least one gas cell enclosing an amount of the component gas to be detected in the at least one optical path in series with the sample chamber. The method further includes determining a mathematical relationship between radiation detected in the at least one optical path and the concentration of a sample gas filling the sample chamber.
The major advantage of the present invention is that gas cell(s) can be permanently embedded in the optical paths of the device. Therefore, gas analyzers with no moving parts can be effectively implemented.